resemble those of the arteries. The same three coats exist and the same
elements enter into their structure. The transition from capillary to
small veins, and from those to larger veins, is similar to the
transition from the arteries to capillaries, in inverse order. The walls
are not so thick as those of arteries. The elastic tissue is much less
in quantity and in smaller veins disappears. There is not a clear line
of demarcation between the intima and the media.
The veins of birds differ from those of mammals in that they have fewer
_valves_. The valves are also less perfect, and often permit a backward
flow of blood.
The walls of the arteries and of the veins are supplied with nutrient
blood-vessels. These are called the _vasa vasorum_, or blood-vessels of
the blood-vessel wall. They are mostly in the adventitia. They may arise
from the vessel to which they are distributed or take origin from an
adjacent vessel. These small arteries supplying the vessel coat after
terminating into capillaries form small veins through which the blood,
from the structure of the vessel wall, is returned.
The walls of the blood-vessels are supplied with both medullated and
non-medullated nerves. The non-medullated nerve fibers are axones of the
sympathetic neurones and control the caliber of the vessels. These
fibers are called the _vasomotor nerves_. They form plexuses in the
adventitia, from which are given off branches which penetrate the media
and terminate on the muscle cells. The medullated nerves are the axones
of the spinal nerves. The larger fibers are found in the connective
tissue outside the adventitia and give off branches to the media where
they divide repeatedly, lose their sheath, and terminate in the media
and at times in the intima.
THE ARTERIAL TRUNKS
The _common aorta_ is short; it originates from the left ventricle (Fig.
61_B_, No. _K_, 14), and is guarded by three _semi-lunar valves_. The
aorta breaks through the pericardium just to the right of the pulmonary
arteries in a ventral direction; it then turns upward dorsally and to
the right of the inferior bodies of the vertebræ. It is then directed
anteriorly, and dorsally to the right bronchus, between the right
bronchus and the right lung. The right and the left coronaries are given
off from the common aorta; they have been discussed. There is next given
off the left brachio-cephalic or _brachio-cephalic sinister artery_
(Fig. 61_B_, No. _K_, 10), which is just above the border of the base of
the heart. This artery passes upward and slightly forward, over the
center of the inferior larynx. Just beyond this point the _subclavian
artery_ is given off; this artery later becomes the axillary and the
axillary the brachial artery. Then there is given off the anterior and
the posterior thoracic arteries; and finally, the pectoral, which supply
the pectoralis muscles and later terminate in the carotid, the
vertebral, and the cervical arteries. The carotid artery gives off an
esophageal artery. The other arterial trunk given off from the common
aorta is the right brachio-cephalic or brachio-cephalic dexter (Fig.
61_B_, No. _K_, 18). The right brachio-cephalic artery gives off the
subclavian, which continues as the axillary, and continues as the
brachial artery. There is given off the anterior and the posterior
thoracic, the right carotid (Fig. 61_B_, No. _K_, 11), the vertebral,
and the dorsal. The last continues as the cervical.
[Illustration:
FIG. 61_B_.
_K._ The arterial trunks. 1, The middle sacral artery. 2, The
hypogastric
artery. 3, The posterior mesenteric artery. 4, The ischiadic artery.
5, The
femoral artery. 6, The renal artery. 7, The left pectoral artery or
thoracico
caudalis. 8, The left axillary artery. 9, The left carotid artery. 10,
The left
brachio-cephalic artery. 11, The right carotid artery. 12, The right
brachial
artery. 13, The right pectoral artery. 14, The common carotid artery.
15,
The posterior aorta. 16, The celiac axis. 17, The anterior mesenteric
artery.
18, The right brachio-cephalic artery. 19, The auricular portion of
the heart.
20, The ventricular portion of same. 21, Sterno-clavicular artery. 22,
Anterior
thoracic.
_L._ The venous trunks. 1, The caudal vein. 2, The coccygeo-mesenteric
vein. 3, The posterior mesenteric vein. 4, The anterior mesenteric
vein. 5, The gastro-duodenal vein. 6, The portal vein. 7, The
hepatic vein. 8, The left anterior vena cava. 9, The left pectoral
vein. 10, The left brachial vein. 11, The left jugular vein. 12, The
right jugular vein. 13, The right brachial vein. 14, The right
pectoral vein. 15, The right anterior vena cava. 16, The posterior
vena cava. 17, The common iliac vein. 18, The femoral vein. 19, The
renal vein. 20, The internal iliac vein. 21, The hypogastric vein.
22, The auricular portion of the heart. 23, The ventricular portion
of same.
]
The _pulmonary arterial trunk_ is given off from the conus arteriosus of
the right ventricle. It is guarded at its origin by three semi-lunar
valves similar to those of the aorta. The trunk divides into two
pulmonary arteries, which are short, one called the pulmonalis dexter
and the other the pulmonalis sinister. The former goes to the right and
the latter to the left lung. Each branch penetrates the lung near the
bronchus. These arteries divide, or branch, similarly to the bronchi.
Following the branchings of the bronchi, they finally terminate into the
lung capillaries, forming networks on the bronchi and the air-tube
terminals.
BRANCHES OF THE BRACHIO-CEPHALIC ARTERY
( Thyroidea
( ( Cervicalis inferior
( Vertebralis ( Vertebralis anterior
( ( Vertebralis posterior
( ( Arteria cervicalis ascendens
( Bronchiales
( Truncus ( Inferior esophageal
( caroticus ( Subcutaneous colli
( ( ( Carotis cerebralis
( ( Carotis ( Cervicalis superior
( ( communis ( Occipitalis
( ( ( Carotis externa
( ( Spinalis anterior ( Basilaris ( Cerebelli inferior
Brachio-cephalic (
( ( Clavicularis
( ( Sterno-clavicularis ( Sternalis
( ( ( Acromialis
( (
( ( ( Subscapularis
( ( ( ( Ulnaris
( Subclavia ( Axillaris ( Brachialis ( Brachialis
profunda
( ( ( Radialis
( ( Humeralis ( Circumflex humeralis
( ( ( anterior
(
( ( Thoracica externa
( Thoracalis ( ( Arteria thoracica
( Thoracica inferior (
longa
(
( Mammaria interna
( Circumflex humeralis posterior
Brachialis profunda ( Collateral ulnaris
( Collateral radialis
The cord-like remnant of the _ductus botalli_, or embryonal connection
between the lung arterial trunk and the anterior aorta, has been
observed but is rare in grown birds.
The arteries, the veins, and the lymphatic vessels of birds anastomose
far more frequently than those of mammals.
BRANCHES OF THE ARTERIA CAROTIS CEREBRALIS INTERNA
( Occipitalis ( Occipitalis sublimis
( ( Occipitalis profunda ( Meningea
( ( Temporalis
( ( ( Rete temporale
( Ophthalmica ( Recurrent ophthalmicum ( Rete
ethmoidalis
( externa ( Ethmoidalis
( ( Plexus palpebralis
( ( Plexus alveolaris inferior
( ( Plexus muscularis
Carotis cerebralis ( Plexus temporalis ( Plexus lacrimalis
( ( Ramus ciliaris posticus
( ( Meningea media
(
( ( Sphenoidea ( Ethmodalis
( ( Spheno-maxillaris ( Ethmoidalis ( externa
( ( ( Ophthalmica ( ( Ethmoidalis
( ( ( interna ( ( interna
( Cerebralis ( (
( Ramus ( Sylviæ
( anterior ( Cerebralis profunda (
Choroid plexus
( Arteria centralis retinæ
( Ramus posterior
BRANCHES OF THE ARTERIA CAROTIS EXTERNA
( Hyoidea
Carotis externa ( Laryngea superior
( Facialis
( Lingualis
BRANCHES OF THE ARTERIA CAROTIS FACIALIS
( Auricularis
Facialis ( Facialis interna ( Alveolaris inferior ( Mentalis
( Maxillaris interna
( Facialis externa
BRANCHES OF THE CAROTID TRUNK
The =carotis communis= artery springs from the carotid trunk of the
brachio-cephalic. It is directed horizontally, ascending to the ventral
side of the neck. It then extends downward to the inferior median neck
region. Just after leaving its origin it gives off several small
branches to the bronchi and to the esophagus, and extends toward the
head. The carotid lies on the thyroid gland and at this point touches
the jugular vein (Fig. 21). At this point the =thyroid arteries= are
given off from the carotid trunk. The thyroid gland also receives blood
from the bronchialis artery.
Dorsalward and near the thyroid gland the carotid artery gives off a
branch (the bronchialis) which accompanies the recurrent laryngeal
nerve, along the inferior larynx and the bronchi, and supplies the lung
substance and that part of the esophagus in this region.
The =vertebral artery= is given off from the carotid trunk, dorsalward
to the thyroid gland, and on the left side. The right vertebral artery
may be given off from the brachialis dextra or right brachialis.
The =inferior esophageal artery= is given off from the ventral side of
the carotid, supplies the esophagus, extends then to the skin of the
neck and to the trachea, is directed anteriorly toward the head and
anastomoses with the vertebral artery. This artery accompanies the vagus
nerve and forms a collateral artery to the carotid and the vertebral
artery.
The =subcutaneous colli= springs from the carotid artery near the
thyroid gland and communicates with the inferior cervical artery, which,
in turn springs from the vertebral artery.
=The Common Carotid.=—Near the last cervical vertebra the two carotid
arteries occupy the same channel, to which they are attached by fascia,
and, lying close to the inferior surface of the bodies of the cervical
vertebræ, are covered by the colli muscles. Near the third or the fourth
cervical vertebra, the two carotid arteries separate. Near the atlas
each carotid divides into the _carotis cerebralis_ and _carotis
externa_. Near this division the _superior cervical artery_ branches
off. This latter artery extends down the neck in company with the
pneumogastric nerve and the jugular vein, supplies the skin and the neck
muscles, and anastomoses with the inferior cervical artery and the
subcutaneous colli artery.
The _occipital artery_ originates either from the carotis communis or
sometimes from the superior cervical.
BRANCHES OF THE CAROTIS CEREBRALIS
The branches of the carotis cerebralis are as follows:
1. The =occipitalis= (Fig. 72, No. 18), which in turn gives off, first,
the occipitalis sublimis. The _occipitalis sublimis_ supplies the outer
and the middle portion of the digastricus and the posterior
mylo-hyoideus muscle. It also gives off, second, the _occipitalis
profunda_ which supplies the inner portion of the digastricus muscle and
becomes the _meningeal artery_, which passes through the foramen vagi,
entering the brain cavity, where it supplies the coverings of the brain
as far as the sella turcica. Superficial branches of this artery are
distributed to the muscles in the region of the atlas and anastomose
with the vertebral artery.
2. The =ophthalmica externa=, which passes below the articulation of the
quadrate bone, around the tympanic cavity, enters the canalis caroticus,
and passes into the cranial cavity. The ramus occipitalis, passing out
of the same foramen, again enters the diploë of the cranium; then after
passing dorsally over the upper outer semicircular canal of the ear,
passes backward through the occipital bone.
The ophthalmica externa (Fig. 72, No. 9) forms a main trunk and gives
off two branches: the _temporal artery_ and the _recurrent ophthalmic_.
The recurrent ophthalmic gives off the _rete temporalis_, _rete
ethmoidalis_, a branch to the orbital gland, and finally anastomoses
with its own branches and with those of the internal ophthalmic at the
olfactory foramen and aids in forming the _ethmoidal artery_. These
arteries supply blood by giving off branches to the muscles of the eye,
sclerotic coat, iris, choroid coat, and the ciliary bodies. It gives off
another branch to Harder’s gland, and finally anastomoses with the
ethmoidalis.
3. The =plexus temporalis=, rete mirabile ophthalmicum, or wonderful
network (Fig. 72, No. 8), is formed between the second and the third
trunk of the trigeminus nerve and the rete ophthalmicum.
Inferior to this is the _alveolar plexus_, which plexus accompanies the
third branch of the trigeminus into the lower jaw. Two main branches
form this plexus, one coming from the carotis facialis, which
anastomoses with the alveolar artery.
The _palpebral plexus_ lies between the trunks of the trigeminus, and
supplies mainly the lower eyelid.
The _plexus muscularis_ extends to the fifth portion of the temporal
muscle.
The _plexus lacrimalis_ forms on the posterior orbital wall on the ramus
ethmoidalis and supplies the lacrimal gland and the upper eyelid. It
anastomoses with branches from the facial artery.
The _ramus ciliaris posticus_ supplies the inferior rectus and the
external rectus muscle of the eyeball. It anastomoses with the
ophthalmica externa.
The _median meningeal artery_ passes through the foramen occupied by the
second branch of the trigeminal nerve. Passing into the cranial cavity,
it supplies the dura mater. Before passing into this foramen, small
branches are given off, which supply the skin and the temporal muscle;
and some branches anastomose with the superior cervical and the
ethmoidal arteries.
=4. The Cerebral Artery.=—Each cerebral artery enters the cranial cavity
through the canalis caroticus located in the sphenoid bone, passes
forward medially from the cochlea, dorsally from the Eustachian tube,
and passes through a small canal which opens on the inner surface of the
sella turcica. Originating in this foramen, the _sphenoid artery_
divides into two branches which anastomose with the pterygoidean and the
pterygo-pharyngeal artery and which supply the upper jaw and the throat
regions.
The _spheno-maxillaris artery_ supplies the gums.
The right and the left cerebral arteries unite at the sella turcica.
After this union they divide again immediately and pass to the base of
the brain, where they give off twigs to the optic nerve, to the optic
chiasm, and where also is given off the arteria retinæ centralis.
Passing posteriorly each cerebral artery gives off the _ramus
posterior_, and then passes to the side of the cerebellum.
The _basilar artery_, a continuation of the anterior spinal artery, is
located ventrally and mesially to the cerebellum. Laterally and
inferiorly the basilar artery gives off the inferior cerebellar artery.
The _ramus anterior_ is given off from the cerebralis artery and
continues as the _internal ophthalmic artery_. The ramus anterior also
gives off the _sylvian artery_, which supplies the sides of the cerebrum
and the middle brain. In the fissure between the hemispheres and the
optic thalamus is located the _arteria cerebri profunda_. This artery
passes along the median surface of the cerebrum and in its course
supplies the adjacent parts. It enters into the formation of the choroid
plexus of the lateral ventricle.
The _internal ophthalmic artery_ extends out of the cranial cavity,
through the optic foramen, into the orbital cavity. It passes upward
along the interorbital wall and supplies the optic nerve, the trigeminus
nerve trunk, and the eye muscles, and dorsally anastomoses near the
olfactory nerve with the rete ethmoidale and the external ophthalmic
artery, and continues as the ethmoidal artery.
The _ethmoidal artery_ supplies the supra-orbital gland and the gland of
Harder. It gives off twigs to the rete ophthalmicum and other branches
to the skin of the frontal region, where it anastomoses with branches of
the external facial artery. These branches in the frontal region are
rather large. Large branches are given off to the comb.
The _arteria ethmoidalis externa_ originates in the nasal cavity from a
division of the ethmoidal artery.
The external ethmoidal artery passes below the lacrimal bone, extends
forward, supplies the walls of the nasal cavity, and finally sends a
branch anteriorly into the upper median portion of the jaw bone, and
other branches to the septum nasi and other parts of the nasal cavity.
There are frequent anastomoses between the ethmoidalis interna, the
facialis, and the spheno-maxillary artery.
The _internal ethmoidal_ artery supplies principally the posterior
turbinated bones and septum nasi.
BRANCHES OF THE EXTERNAL CAROTID ARTERY
Branches from the external carotid and the facial artery supply the
tongue and its muscles, the larynx, the lower jaw bone, the gums, and
the upper lateral facial region.
The external carotid (Fig. 62, No. _A_, 8) gives off the following
branches:
First, the =hyoid artery= (Fig. 72, No. 12) which supplies the inner
portion of the depressor mandibular and also the cornua of the os
hyoideum, and extends to the tip of the tongue.
Second, the =superior laryngeal artery= (Fig. 72, No. 16) which supplies
the sterno-brachialis and gives off branches which extend downward to
the trachea and to the esophagus. The main artery passes along the left
side of the esophagus and anastomoses with branches of the inferior
esophageal, forming collateral circulation in that region.
[Illustration:
FIG. 62.
_A._ Blood-vessels of the head. 1, The cerebellum. 2. The cerebrum. 3,
The semicircular canals. 4, Sinus occipitalis superior. 5, Sinus
temporalis sphenoideus. 6, Sinus transversus dexter. 7, Superior
esophageal artery. 8, Carotis externus. 9, Lingual artery. 10, Sinus
longitudinalis.
_B._ Veins of the antero-inferior part of the head and neck. 1, The
right carotid artery. 2, The left carotid artery. 3, Vena jugularis
dexter. 4, Vena vertebralis dexter. 5, Transverse vein. 6, Vena
cephalica dexter anterior. 7, Vena lingualis. 8, Vena cephalica
posterior. 9, Vena facialis externa dexter. 10, Vena infrapalatina.
11, Posterior nares. 12, Vena facialis interna. 13, Vena facialis
externa sinister.
_C._ The brain. 1, Medulla oblongata. 2, Cerebellum. 3, Optic lobe. 4,
Cerebrum. 5, Longitudinal fissure. 6, Transverse fissure. 7,
Olfactory nerve. 8, Optic nerve. 9, Optic commissure. 10, Motor
oculi. 11, Patheticus. 12, Trigeminal, or trifacialis. 13, Abducens.
14, Facialis. 15, Auditory, or acousticus. 16, Glosso-pharyngeus.
17, Pneumogastric. 18, Spinal accessory. 19, Hypoglossus. 20,
Hypophysis. 21, Crus cerebri. 22, Ganglion on superior nerve trunk.
23, Spinal cord. 24, A pair of spinal nerves.
]
Third, the =lingualis artery= (Fig. 62, No. _A_, 9) which lies between
the mylo-hyoideus and the posterior part of the hyoid bone. It supplies
the tongue muscles. It passes to the median surface of the lower jaw
bone, where are given off small branches which enter the jaw and
anastomose with the inferior alveolar artery.
Fourth, the =Facial Artery=.—The facial artery divides into the
following branches:
The _auricular artery_ is given off near the articulation of the os
quadratum with the os zygomaticum. It is located at the outer auditory
canal, and its branches are distributed to the parotid region and to the
depressor mandibular, or digastricus, muscle.
The _external facial artery_ is located between the os quadratum and the
masseter muscle. It gives off a branch to the lower jaw bone and to the
skin of that region, and then passes to the lacrimal bone and supplies
branches to the commissure of the mouth, the auditory canal, the
masseter muscle, the three eyelids (upper and lower eyelids and the
membrana nictitans), the nose cavity, and the skin in the frontal
region. It communicates on the other side with the ethmoidal artery.
The _internal facial artery_ passes over and through the os
pterygoideum, supplies all the jaw muscles, and is continued as the
inferior alveolar artery.
The _inferior alveolar artery_ enters the canal of the lower jaw bone
along with the mandibular nerve. It is finally continued as the mental
artery, leaving the canal, and passing to the outer jaw surface.
The facialis continues as the _internal maxillary artery_.
The internal maxillary artery (Fig. 72, No. 15) supplies the pterygoid
muscle, the upper part of the pharynx, the commissure of the mouth, the
salivary gland region, the gums, and finally anastomoses with branches
of the spheno-maxillaris artery.
BRANCHES OF THE VERTEBRAL ARTERY
The vertebral artery is given off, dorsally near the thyroid gland, from
the carotis communis or from the carotid trunk. The vertebral artery
passes horizontally and dorsally into the canals formed in the
transverse processes of the cervical vertebræ. After it leaves the
carotid, it is divided into anterior and posterior branches.
The =posterior vertebral artery= passes in the canals of the transverse
processes of the fifth or sixth dorsal vertebra. It sends branches into
the vertebræ, into the spinal canal, and into the intercostal muscles
between the ribs and anastomoses with the intercostal arteries.
The =anterior vertebral artery= is larger than the posterior. It extends
laterally along the side of the neck in the foramen of the transverse
processes of the cervical vertebræ, and lies along the course of the
inferior vertebral vein and the deep imbedded trunk of the sympathetic
nerve. It continues to the head. In its passage it gives off to each
vertebral segment a dorsal and a ventral branch. Twigs from these
branches pass into the bodies of the vertebræ and the spinal canal,
giving nutriment to the bony structure and to the spinal cord and its
coverings. Other twigs are distributed to the muscles of the neck and
some finally anastomose with branches of the carotis communis. This
artery, reaching the head, gives off a long anastomosing branch which
passes between the atlas and posterior part of the occipital bone and
joins the ramus profundus and the occipital artery, thus again
communicating with the carotid artery. The remainder of the vertebral
artery is small and passes through the foramen magnum into the cranial
cavity where it anastomoses with terminal branches of the cerebral
artery. At the base of the neck and before the vertebral artery enters
the canal of the cervical vertebræ, it gives off the _arteria cervicalis
ascendens_, superior artery of the crop (Fig. 73, No. 18) which branches
out on the upper surface of the crop is also distributed to the neck
muscles, and later subdivides into the transverse cervical arteries
which supply the skin and the muscles of the base of the neck, and the
shoulder region.
On the ventral side of the neck there are given off two subvertebral
carotid arterial branches. They lie in a shallow furrow on the ventral
side of the cervical vertebræ and close to the median line.
BRANCHES OF THE SUBCLAVIAN ARTERY
The subclavian artery (Fig. 20, No. 13; Fig. 73, No. 11) gives off the
following branches:
1. =Sterno-clavicularis= (Fig. 73, No. 9) which originates on the upper
part of the subclavia, between the carotid artery and external thoracic
(Fig. 73, No. 3), divides into many branches. The sterno-clavicularis
gives off the _sternal artery_, which enters by the side of the
supra-coracoid muscle and the anterior rim of the sternum. It is
distributed to the inner surface and over the air-sac. Another outside
branch passes the posterior end of the crista sterna and supplies the
large breast muscles.
The _clavicular artery_ (Fig. 73, No. 8) accompanies the clavicle to the
shoulder-joint.
The _acromial artery_ is given off from the sterno-clavicularis on the
ligament near the shoulder-joint.
2. The =thoracic artery= branches from the subclavian artery (Fig. 70,
No. 4). The thoracic artery gives off the following branches:
The _internal mammary_, or _internal thoracic artery_ (Fig. 73, No. 16)
arises on the inner side of the sternum and extends downward and
backward, giving nutrient branches to the anterior vena cava and to the
diaphragm. At the point of the costo-sternal muscle it divides into an
inner and an outer branch.